Catheters are elongate tubular devices sized for introduction into body passages and cavities of a patient, such as a patient's vascular system, gastrointestinal system, abdominal cavity, and the like. A catheter may include one or more lumens intended for passing various other devices, agents, and/or fluids into a body lumen or cavity accessed by the catheter. In most instances, especially within a patient's arterial system, and most especially in the chambers of the heart, ingress of air is highly undesirable since such bubbles may cause stroke or infarct of tissue, including cardiac tissue. Generally, catheter lumens are flushed to attempt to remove any air before a procedure, and valves are provided to prevent additional ingress of air into the lumens during a procedure.
The properties of the inner surface of one or more lumens of the catheter may significantly impact the performance of the catheter. In particular, the lubricity of the inner surface may affect the ability to pass other devices, agents, and/or fluids through the lumen(s) of the catheter.
To enhance lubricity, it has been suggested to include polytetraflouroethylene (“PTFE”), polyethylene (“PE”) or other cores surrounding the lumen of a catheter. The inner core may be intended to provide a lubricious inner surface to facilitate passing guidewires, pacing leads, or other devices through the lumen of the catheter. Constructing such a catheter, however, is complicated because of the difficulty bonding the inner core to the outer portions of the catheter.
For example, PTFE, in its native form is nearly impossible to bond; consequently, it must be held in place by mechanical interaction or must be etched in order to impart bondability. Further, because of the inaccessibility of the inner surface of the lumen of a catheter, mechanical abrasion or modification, cleaning, etching, application of adhesive, or other modifications of the inner surfaces to facilitate bonding are generally difficult to complete. Furthermore, materials such as PTFE may degrade under commonly used sterilization techniques, such as gamma sterilization, and therefore may be inappropriate for certain catheter devices. PE, similar to PTFE, is also difficult to bond to other materials. In some cases, a third material must be used that is bondable both to PE and to other plastics. In both cases, the manufacturing process is complicated and the materials generally expensive.
Other methods for imparting lubricity to inner surfaces have been tried, for example, vapor deposition of surface coatings such as Parylene; however, this process is also complicated and does not result in optimal lubricity.
Hydrophilic coatings are well known and are widely used in medical devices. These are readily applied to outer surfaces and frequently used on exteriors of catheters, for example, to facilitate tracking through the vasculature. However, application of these and other coatings to inner surfaces is currently significantly hindered by technical challenges and therefore not widely practiced.
The majority of catheter materials used in construction of catheter liners or other lumen inner surfaces (e.g., PTFE, PEBAX, Nylon) are significantly or modestly hydrophobic. As such, air bubbles—relative to the saline or blood based infusates—are more attracted to the catheter material inner surface than the saline or blood based infusates are to the same material. Thus, air bubbles may tend to stick to the catheter lumen inner surfaces and may be resistant to removal/extraction even during additional flushing. If such air bubbles were to remain in this position during a medical procedure, there would not be a clinical problem. However, there may be substantial risk that such air bubbles are subsequently displaced mechanically, i.e., when secondary devices are passed through the lumens.
For example, in the case of a dilator, many bubbles may be removed during dilator insertion (frequently done outside the body), however there is substantial risk that some may remain within the lumen. When additional devices are passed through the lumen during the procedure (e.g., after removing the dilator), residual bubbles may be displaced through the catheter and into the patient's bloodstream or other body lumen. This is especially true with tight fitting devices, such as balloon catheters.